Radioactive decay and half-life: Edexcel International A Level Physics questions

Every Edexcel International A Level Physics exam question on Radioactive decay and half-life (specification points 137–142), 2019–2025, with its mark scheme and examiner’s report.

All 84 questions on Radioactive decay and half-life, as a list

June 2025, Unit 5, Q6 (1 mark): In a laboratory, the background count rate is 22 counts per minute. A detector is placed 25 cm from a gamma source. The count rate recorded by the detector is 5
June 2025, Unit 5, Q7 (1 mark): A student used a detector to determine the intensity of radiation from a source of gamma radiation. After correcting for background, the intensity of radiation
June 2025, Unit 5, Q12 (4 marks): The photograph shows a student observing the tracks of alpha particles and beta particles in a cloud chamber. (Source: © NASA Archive/Alamy Stock Photo) The par
June 2025, Unit 5, Q20(a) (2 marks): Complete the nuclear equation for the decay of plutonium‑238. (2) 238 Pu → 92 U + α
June 2025, Unit 5, Q20(b)(ii) (5 marks): When the space probe was launched, the decay of plutonium‑238 produced a power of 550 W. A website states that there was 1.00 kg of plutonium‑238 when the space
June 2025, Unit 5, Q20(b)(iii) (2 marks): The space probe took 74 months to travel to Jupiter. Calculate the power produced when the space probe arrived at Jupiter, due to the decay of plutonium‑238. 1
January 2025, Unit 5, Q21(a)(i) (2 marks): Explain why a source of beta radiation is suitable to monitor the thickness of the paper. (2)
January 2025, Unit 5, Q21(a)(ii) (2 marks): Pm‑147 decays by beta decay to an isotope of samarium, Sm. Complete the decay equation. (2) 0 νe– 147 − + 0 61Pm → Sm + β
January 2025, Unit 5, Q21(a)(iii) (4 marks): In a particular paper mill, the Pm source was replaced when the activity of the source had decreased to 0.75% of its initial activity. Calculate the time that t
October 2024, Unit 5, Q1 (1 mark): A radioactive source emits alpha radiation, beta radiation and gamma radiation. Which of the following is correct? A Alpha radiation is the most ionising. B Bet
October 2024, Unit 5, Q21(a)(i) (2 marks): Complete the nuclear equation for the decay of uranium-241. (2) 241 − 92U → Np + β
October 2024, Unit 5, Q21(b) (4 marks): The half-life of uranium-241 is 40 minutes. The half‑life of uranium-242 is 17 minutes. Initially, a sample has the same number of uranium-241 atoms as uranium-
June 2024, Unit 5, Q5 (1 mark): Which of the following correctly describes the random nature of radioactive decay? A Radioactive decay is a natural process. B Radioactive decay is a spontaneou
June 2024, Unit 5, Q14(a) (1 mark): Americium emits alpha radiation as well as gamma radiation. State why alpha radiation will not affect the recorded count rate. (1)
June 2024, Unit 5, Q14(b) (2 marks): Explain one modification to her method that would give a more accurate value for the count rate. (2)
June 2024, Unit 5, Q14(c) (3 marks): The student plotted a graph of count rate R against thickness x of absorber. Her graph is shown below. 70 60 50 40 R / s–1 30 20 10 0 0.0 1.0 2.0 3.0 4.0 5.0 x
June 2024, Unit 5, Q17(a) (2 marks): Complete the nuclear equation for the decay of 131I. (2) 131 − + 0 53I → Xe + β 0νe
June 2024, Unit 5, Q17(b)(i) (6 marks): For one treatment, the suggested activity to be used is 51.8 MBq kg –1. The mass of the patient is 65 kg. Calculate the mass of 131I required to treat this pati
June 2024, Unit 5, Q17(b)(ii) (2 marks): For another treatment, a sample of 131I with an activity of 2.35 GBq is required. The sample is prepared 24 hours before it is required. Calculate the activity
January 2024, Unit 5, Q5 (1 mark): Which of the following correctly describes the spontaneous nature of radioactive decay? A Radioactive decay is a natural process. B Radioactive decay is a rando
January 2024, Unit 5, Q19(c)(i) (2 marks): Complete the nuclear equation for the decay of strontium–90. (2) 0 90Sr → Y + β – + 0ve 38
January 2024, Unit 5, Q19(c)(ii) (3 marks): In Georgia, in December 2001, some men discovered two small canisters in a forest. The canisters were hot and had melted surrounding snow. The canisters 90Sr. w
January 2024, Unit 5, Q19(c)(iii) (3 marks): The authorities claimed that the canisters were 50 years old. The activity of each 15 Bq. canister when new was 3.700 × 10 Assess the accuracy of the claim. 90S
January 2024, Unit 5, Q20(a) (4 marks): A teacher tested an unknown radioactive source. He set up the source and a GM tube, as shown. GM tube source The initial count rate is determined without an abs
January 2024, Unit 5, Q20(b) (5 marks): The count rate R recorded after gamma radiation has passed through a thickness x of lead is given by –μx R = R0e where R0 is the count rate with no absorber pre
October 2023, Unit 5, Q8 (1 mark): Which row of the table gives the relative ionising power and penetration of gamma radiation? Ionising power Penetration A low low B low high C high low D high h
October 2023, Unit 5, Q19(a)(i) (2 marks): Show that the decay constant for caesium-137 is about 7.3 × 10 –10 s –1. half‑life of caesium-137 = 30.1 years 1 year = 3.15 × 10 7 s (2)
October 2023, Unit 5, Q19(a)(ii) (3 marks): Calculate the mass of caesium in the capsule. (3) Mass of caesium =
October 2023, Unit 5, Q19(a)(iii) (2 marks): Calculate the activity of the caesium in the capsule after 2 years. (2) Activity after 2 years =
October 2023, Unit 5, Q19(b) (3 marks): The capsule was found after 14 days. Calculate the total energy, in J, released from the capsule in 14 days. activity of caesium in capsule = 19 GBq energy rele
June 2023, Unit 5, Q7 (1 mark): A student is investigating the absorption of gamma radiation by lead. Before starting the investigation, she determines the background count. Which of the follo
June 2023, Unit 5, Q11(a) (2 marks): Complete the nuclear equation for the decay of rhenium-187. (2) 0 v– 187 – + 0 75Re → Os + β
June 2023, Unit 5, Q11(b) (3 marks): The energy released in the decay is 2.6 keV. You may assume that, in this case, the beta particle receives all the emitted energy. Calculate the speed of a β –
June 2023, Unit 5, Q13 (4 marks): A cloud chamber is used to show the tracks of alpha particles and beta particles. These particles ionise the air as they pass through the chamber. Liquid drople
June 2023, Unit 5, Q16(b) (4 marks): Determine the time taken, in years, for 90% of the thorium-230 in a sample to decay to radium-226. half-life of thorium-230 = 75 400 years (4) Time taken = year
June 2023, Unit 6, Q2(a) (2 marks): State two safety precautions for this investigation. (2)
June 2023, Unit 6, Q2(b)(i) (2 marks): Explain why a graph of ln C against x could be used to test the validity of this relationship. (2)
June 2023, Unit 6, Q2(b)(ii) (6 marks): Devise a plan to obtain the data required to test the validity of this relationship. (6)
January 2023, Unit 5, Q1 (1 mark): A student used a detector and counter to measure the background radiation count for five minutes. He used this value to calculate the background count rate. Whi
January 2023, Unit 5, Q7 (1 mark): A student investigated the absorption of gamma radiation by lead, as shown. lead absorber GM tube gamma source With no absorber the intensity of radiation was I
January 2023, Unit 5, Q15(a) (2 marks): 137Cs decays to an isotope of barium by emitting a β – particle. Complete the nuclear equation for the decay of 137Cs. (2) 137Cs → 0 − + 56Ba + β 0ve
January 2023, Unit 5, Q15(b) (4 marks): A sample of pure 137Cs has an activity of 7400 Bq. Calculate the mass, in kg, of the sample. half‑life of 137Cs = 30.2 years mass of 137Cs atom = 137 u 1 year =
October 2022, Unit 5, Q3 (1 mark): A radioactive source is placed a few centimetres away from a detector. When a sheet of paper is placed between the source and the detector there is no change in
October 2022, Unit 5, Q5 (1 mark): The radioactive decay of a nucleus is described as a random process. Which of the following is a reason for this? A There are a number of different decay paths.
October 2022, Unit 5, Q20(b)(i) (2 marks): Caesium-137 decays by emitting beta radiation. Complete the nuclear equation for the decay of caesium-137. 0 ν– 55 Cs → Ba + ꞵ– + 0 137 (2)
October 2022, Unit 5, Q20(b)(ii) (2 marks): Explain why the emission of an antineutrino in the decay leads to a range of energies for the ꞵ– particles. (2)
October 2022, Unit 5, Q20(c)(i) (6 marks): A nuclear fission reactor produces about 24 kg of caesium-137 each year. A website states that 24 kg of caesium-137 has the same activity as 2000 kg of radium-2
October 2022, Unit 5, Q20(c)(ii) (3 marks): Caesium-137 may enter plants grown in a contaminated area. The radiation from 100 g of plant material grown in a contaminated area can have a count rate as high
June 2022, Unit 5, Q9 (1 mark): Bismuth decays to form a stable isotope of thallium. Which graph shows how the number N of thallium atoms in a sample of bismuth varies with time t? N N N N t t
June 2022, Unit 5, Q13(a) (2 marks): Complete the nuclear equation for the decay of 40K by β– emission. 40 0 K → 20Ca + β– + 0v (2)
June 2022, Unit 5, Q13(c) (3 marks): A fertiliser contains potassium chloride. The activity of a sample of the fertiliser due to radioactive potassium was 48.6 Bq. It is claimed that the time t tak
January 2022, Unit 5, Q4 (1 mark): Tritium is a radioactive isotope. Wine may contain traces of tritium. One 25‑year‑old bottle of wine was found to have an unusually high activity of 22 Bq. half
January 2022, Unit 5, Q7 (1 mark): A student investigates the absorption of gamma radiation by lead. She determines the background radiation count rate before she starts the investigation. Which
January 2022, Unit 5, Q14 (5 marks): Strontium-90 is commonly used in schools to demonstrate the properties of β particles. The range of energies of β particles emitted from a source of strontium-9
January 2022, Unit 5, Q20(a) (2 marks): Complete the nuclear equation for this decay. 225 89Ac → Fr + α (2)
January 2022, Unit 5, Q20(d) (4 marks): The activity of a sample of actinium‑225 is 7.4 × 107 Bq when it is prepared. Calculate the number of actinium atoms in the sample 7.0 days later. half‑life of
January 2022, Unit 6, Q3(a) (2 marks): State two precautions that should be taken when using this source. (2)
January 2022, Unit 6, Q3(b) (2 marks): The radiation emitted from a radioactive source can be investigated using the apparatus shown. The Geiger-Muller (GM) tube detects beta radiation and gamma radi
January 2022, Unit 6, Q3(c) (2 marks): The corrected count rate C varies over time t according to the relationship C = C0 e−λt where C0 is the initial count rate and λ is the decay constant. Explain
January 2022, Unit 6, Q3(d)(i) (5 marks): Plot a graph of ln C against t on the grid opposite. Use the additional column in the table to record your processed data. (5)
January 2022, Unit 6, Q3(d)(ii) (3 marks): Isotope X has a half-life of approximately 30 minutes. Determine a value of λ, in hours−1, for isotope Y. (3) λ = hours−1
January 2022, Unit 6, Q3(d)(iii) (2 marks): Hence determine the half-life t½ for isotope Y. (2) t½ =
October 2021, Unit 5, Q4 (1 mark): Cancer cells inside the body can be killed by directing narrow beams of radiation from different directions onto the cells. The source of radiation is outside t
October 2021, Unit 5, Q6 (1 mark): Polonium‑218 is a naturally occurring radioactive isotope with a half-life of 185 s. A sample of this isotope contains 2.75 × 1015 unstable nuclei. Which of the
October 2021, Unit 5, Q19(a)(i) (2 marks): Complete the nuclear equation for the decay of cobalt-60 to nickel. 60 0 27Co → Ni + β− + 0ve (2)
October 2021, Unit 5, Q19(a)(ii) (1 mark): Suggest why the majority of the energy released is shared between the β− particle and the antineutrino. (1)
October 2021, Unit 5, Q19(b) (3 marks): The activity of a cobalt‑60 source is 4.07 × 1014 Bq initially. When used for sterilising, the source is replaced when the activity drops below 1.85 × 1014 Bq.
October 2021, Unit 5, Q19(c) (3 marks): When in use the cobalt-60 source is shielded with lead. The graph shows how the transmission of γ-radiation depends upon the thickness x of the lead shielding.
June 2021, Unit 5, Q1 (1 mark): A detector and counter were placed near a radium source. A student measured the count for one minute. He used this value to calculate the count rate in Bq from
June 2021, Unit 5, Q18(e) (6 marks): Ultraviolet radiation (UV) is produced when alpha particles interact with air. This can be used to detect alpha particles when a nuclear reactor is decommission
June 2021, Unit 5, Q19(b) (5 marks): In one pacemaker, the activity of the plutonium source was measured to be 6.75 × 1010 Bq in 2020. Calculate the power of the source, in W, when it was fitted 40
June 2021, Unit 5, Q19(c) (3 marks): Another source that was used in early pacemakers was promethium-147. This emits β-particles. The energy spectrum for the β-particles is shown. Number of β-parti
January 2021, Unit 5, Q3 (1 mark): The penetration of matter by radiation depends on the ionising power of the radiation. Which of the following statements is correct? A α-particles are weakly io
January 2021, Unit 5, Q15 (6 marks): A student investigated the absorption of gamma radiation by iron. She placed a gamma source in a holder and set up a Geiger-Müller (GM) tube a short distance aw
January 2021, Unit 5, Q19(a)(i) (2 marks): Complete the nuclear equation for this decay: 40K → 20Ca + 0 β– + 0ve (2)
January 2021, Unit 5, Q19(a)(iii) (2 marks): Explain why there is a range of energies for the beta particles emitted in the decay of a sample of potassium-40. (2)
January 2021, Unit 5, Q19(b)(i) (3 marks): Show that the activity of this sample is about 1.9 ´ 105 Bq. (3)
January 2021, Unit 5, Q19(b)(ii) (2 marks): It is claimed that after a period of 50 years, the activity of the sample would be less than the activity of a typical school source. Assess the validity of thi
October 2020, Unit 5, Q1 (1 mark): A radiation detector is placed near a radioactive source and measures the count rate from the source. Different absorbers are placed between the detector and th
October 2020, Unit 5, Q6 (1 mark): To correct the readings for the effect of background radiation she should A add the background count to each count. B add the background count rate to each coun
October 2020, Unit 5, Q7 (1 mark): The student discovered that a thickness of 1.0 cm of lead reduced the corrected count rate to 50% of its initial value with no lead. Which of the following stat
October 2020, Unit 5, Q18(c) (3 marks): The isotope Og-294 is extremely unstable and decays via alpha decay. After 2.5 ms, a sample contains 500 atoms of Og-294. Calculate the original number of Og-29
October 2020, Unit 5, Q18(d) (2 marks): Explain a precaution necessary when handling a sample of an alpha emitting isotope. (2)
October 2020, Unit 6, Q2 (6 marks): A student wrote the following plan to investigate the distance travelled by alpha particles in air. Place the Geiger-Müller tube in front of the source. Measure

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